Mutations in connexin26 (Cx26) and Cx30 are the most common causes of hereditary deafness in humans. These mutations are one of the most frequently-observed human genetic defects, which are responsible for millions of prelingual severe hearing impairment cases. Although the causal effect of Cx mutations for congenital hearing loss is well established, little is known about mechanisms of hearing impairment caused by the Cx mutations. Currently no mechanism-based therapies are available for deaf patients suffering Cx mutations. Results obtained from last grant period demonstrated that loss-of-function Cx26 mutations arrest normal morphological development of the hearing organ (the organ of Corti), and suggested that a failure to develop endocochlear potential (the battery that powers the hearing transduction) causes deafness in Cx30 mutant mice. In this grant renewal we seek support to further investigate molecular mechanisms and explore novel therapeutic strategies for deafness caused by Cx26 and Cx30 mutations that are linked to human sensorineural hearing impairments. We will test the functional roles of Cx26 in the normal maturation of the organ of Corti. We will rescue hearing of Cx30 null mutant mice by a genetic approach to over-express the Kcnj10 gene that is known to be critical for the development of the normal endolymphatic potential. Results of these studies will have direct implications for human deafness caused by Cx mutations that are responsible for about half of non-syndromic congenital hearing loss cases.